PlayerUnknown's Battlegrounds is coming to Xbox at the end of December and has been very popular on the PC with Steam for a while now. This is a "Battle Royal" game, which is kind of like Hunger Games. You're dropped into a very realistic, large and vivid world with 99 other people. The goal is to get as many weapons as you can, kill as many other people as you can, and be the last player standing. This is interesting because this is an independent game, not from a big game company, and it's hugely successful. Read more at news.xbox.com.
Games are so violent because it's a fairly easy thing to do in software. The first video game you may be familiar with was Pong, which is just two paddles with a square ball that went back and forth. It was easy to do because it's easy to animate the ball and paddles, and collision detection is a simple thing to do in software and hardware. Collision detection became so popular that many games were written with that as its premise, and that naturally extended to projectile weapons hitting targets. Once people started writing those games, they became very popular. The game Doom introduced first-person shooters, where you would see your hands and the weapon as if you were actually in the character you're playing.